As technologies evolve, new internet phone services for mobile devices emerge. In accordance with a specification for providing broadcast services to mobile devices, digital television broadcasting standards may be divided into three major categories. Advanced Television Standards Committee (ATSC) is a standard used in North America. Integrated Service Digital Broadcasting (ISDB) is a standard mainly used in Japan. Digital Video Broadcasting (DVB) is a standard used in European countries. Digital Video Broadcasting-Handheld (DVB-H), as a subset of DVB, is specifically designed to provide mobile broadcasting services to mobile handsets, such as mobile phones.
Each mobile handset may comprise a receiver to handle a variety of mobile standards and corresponding frequency spectra adopted by the variety of mobile standards. There are two prevailing receiver architectures. One is a super-heterodyne architecture, which converts an input signal of a receiver into an intermediate frequency signal so that better receiver performance can be achieved because receiver components such as filters can be optimized to work at the intermediate frequency. The other prevailing receiver architecture is based upon direct conversion. A direct conversion receiver mixes a radio frequency signal with a signal generated by a local oscillator at the radio frequency. The direct conversion receiver further comprises low frequency filters used to eliminate unwanted noise from the mixed signal and convert the mixed signal directly to a baseband frequency signal without an intermediate frequency.
The performance of receiver filters has direct impact on quality of baseband signals. The receiver filters' performance may vary under different operating conditions. For example, due to variations in process, voltage, and temperature (PVT), the bandwidth of a filter may shift out of the range to which it is specified. In order to compensate for the variations due to PVT, a calibration process may be employed to fine-tune the bandwidth of a receiver filter so that the receiver can provide high quality baseband signals.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.